Use of a phosphorus compound as a non-corrosive extreme-pressure and anti-wear additive in a lubricant for a propulsion system of an electric or hybrid vehicle

ABSTRACT

The invention relates to the use of at least one phosphorus compound, which is free of sulfur and has no amine function, as an anti-wear and extreme-pressure additive in a lubricant composition for a propulsion system of an electric or hybrid vehicle. The invention also relates to the use of a lubricant composition comprising at least one phosphorus compound, which is free of sulfur and has no amine function, as an anti-wear and extreme-pressure additive, for lubricating and optionally cooling a propulsion system of an electric or hybrid vehicle, in particular for lubricating and cooling the electric motor and the power electronics of an electric or hybrid vehicle.

TECHNICAL FIELD

The present invention relates to the field of lubricating compositions, more particularly the field of lubricating compositions for a propulsion system of an electric or hybrid vehicle. It relates more particularly to the use in these lubricants of phosphorus compounds free from sulfur and from amine function as advantageously “noncorrosive” extreme pressure and antiwear additives.

The development of international standards for reducing CO₂ emissions, but also for reducing energy consumption, is motivating automakers to propose alternative solutions to combustion engines.

One of the solutions identified by the automakers is to replace the combustion engines with electric motors. Research into reducing CO₂ emissions has therefore led to the development of electric vehicles by some automobile companies.

An “electric vehicle” in the sense of the present invention denotes a vehicle comprising an electric motor as its sole means of propulsion, whereas a hybrid vehicle comprises a combustion engine and an electric motor as combined means of propulsion.

A “propulsion system” in the sense of the present invention denotes a system comprising mechanical components necessary to the propulsion of a vehicle. The propulsion system of an electric vehicle thus encompasses more particularly an electric motor comprising the rotor-stator assembly of the power electronics (dedicated to regulating the speed), a transmission and a battery.

Generally speaking, it is necessary to employ lubricating compositions, also called “the lubricants”, in vehicles for purposes primarily of reducing the frictional forces between the various components of the vehicle's propulsion system, in particular between the moving metal components in the engines. These lubricating compositions are additionally effective in preventing premature wear or even damage to these components, and more particularly to their surface.

To accomplish this, a lubricating composition is conventionally composed of one or more base oils, generally combined with a number of additives whose purpose is to stimulate the lubricating performance of the base oil, but also to provide it with supplementary performance characteristics.

More particularly, additives known as “antiwear” additives are contemplated in order to reduce the wear of the components in the propulsion system, especially of the mechanical components of the motor, and thereby to prevent deterioration in the durability of the motor. There are a wide variety of antiwear additives, examples including dimercaptothiadiazoles, polysulfides, especially sulfur-containing olefins, amine phosphates, or else phosphosulfur additives, such as metal alkylthiophosphates, more particularly zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates or ZnDTP.

The antiwear additives presently employed in lubricants for vehicle motors, such as dimercaptothiadiazoles, zinc dithiophosphate or else polysulfides, have the disadvantage, unfortunately, of being corrosive. Moreover, ionic additives, such as the metal dialkyldithiophosphates, reduce the electrical insulating power of the fluid.

The corrosion problem may prove particularly critical in the context of propulsion systems of electric hybrid vehicles. More particularly, corrosion may give rise to a risk of deterioration affecting the winding of the rotor-stator pairing, sensors in the propulsion system, solenoid valves in the hydraulic system, but also rolling bearings situated between the rotor and the stator of an electric motor, which are generally based on copper and hence particularly sensitive to corrosion, or else affecting gaskets or varnishes present in the propulsion system. In the context of the use of lubricants for drive systems in electric or hybrid vehicles, it is therefore crucial to prevent risks of corrosion.

Moreover, in order to be able to cool the propulsion systems of electric or hybrid vehicles, it is imperative for the lubricant to be an effective electrical insulant, in order to avoid any failure of the electrical components present. More particularly, a conductive lubricant may give rise to a risk of escape of electric current within the winding of the stator and rotor, thereby reducing the efficacy of the propulsion systems, and entailing possible overheating of the electrical components, even going so far as to impair the system. In the context of the use of lubricants for drive systems of electric or hybrid vehicles, it is therefore crucial for the lubricants to have good electrical insulation properties, as well as their noncorrosive properties.

SUMMARY OF THE INVENTION

The present invention aims specifically to propose a means for enhancing the antiwear properties of a lubricant intended for a propulsion system of an electric or hybrid vehicle, while removing corrosion problems encountered in the context of the antiwear systems conventionally used.

The inventors have found more specifically that it is possible to obtain a lubricating composition for a propulsion system of electric or hybrid vehicles that exhibits enhanced antiwear properties, without, moreover, giving rise to a corrosive effect, by employing phosphorus compounds free from sulfur and from amine function as extreme pressure and antiwear additives.

Therefore, according to a first aspect of the present invention, it relates to the use of at least one phosphorus compound, free from sulfur and from amine function, as an extreme pressure and antiwear additive in a lubricating composition intended for a propulsion system of an electric or hybrid vehicle.

An “extreme pressure and antiwear additive” denotes a compound which, when employed in a lubricating composition, especially in a lubricating composition for the drive system of an electric or hybrid vehicle, enhances the antiwear properties of the composition, even under severe pressure and/or temperature conditions.

The antiwear properties of a composition may be evaluated more particularly in accordance with the standard ASTM D2670.

In another of the aspects of the invention, it further relates to the use of a lubricating composition comprising at least one phosphorus compound, free from sulfur and from amine function, as extreme pressure and antiwear additive for lubricating and optionally cooling a propulsion system of an electric or hybrid vehicle, more particularly for lubricating and cooling the electric motor and the power electronics of an electric or hybrid vehicle.

As illustrated in the examples which follow, the inventors have observed that phosphorus extreme pressure and antiwear additives of these kinds, free from sulfur and from amine function, and more particularly of triaryl phosphate ester type, do not induce corrosion when they are in contact with metal surfaces, more particularly those of a propulsion system in an electric or hybrid vehicle, in contrast to aminic and/or sulfur-containing phosphorus antiwear additives.

The corrosive (or corroding) power of a compound may be evaluated by a test which studies the variation in the electrical resistance of a copper wire of predetermined diameter as a function of the time for which this wire is immersed within a composition comprising said test compound in a noncorrosive medium, as for example in one or more base oils. The change in the value of this electrical resistance is correlated directly with the variation in the diameter of the wire tested. Accordingly, in the context of the present invention, a compound is said to be “noncorrosive” when the loss of diameter of the copper wire under study is less than or equal to 0.5 μm after immersion for 80 hours, more particularly less than or equal to 0.2 μm after immersion for 20 hours, in the composition comprising said compound.

The dielectric properties of a lubricant are represented in particular by the electrical resistivity and the dielectric loss (tan δ), which may be measured according to standard IEC 60247.

The electrical resistivity represents the capacity of the material to oppose the circulation of the electric current. It is expressed in ohm-meters (Ω·m). The greater the electrical resistivity, the lower the electrical conduction of the lubricant.

The loss angle δ is the complementary angle of the phase difference between the voltage applied and the altemating current. This factor conveys the losses of energy due to Joule effect. The heating effects are therefore linked directly to the value of δ.

A lubricant intended for use in a vehicle transmission commonly has a tan δ value of the order of unity at ambient temperature. The lower the tan δ value, the greater the electrical insulation of the lubricant.

Said phosphorus compound or compounds, employed as extreme pressure and antiwear additives according to the invention, are advantageously selected from phosphate esters or phosphite esters, more particularly triaryl phosphate esters or triaryl phosphite esters, preferably tri(alkyl-aryl) phosphate or tri(alkyl-aryl) phosphite esters, and advantageously triphenyl phosphate esters or triphenyl phosphite esters.

In a lubricating composition for propulsion systems of electric or hybrid vehicles, the effect possible by introducing one or more phosphorus compounds free from sulfur and from amine function according to the invention is that, advantageously, of enhancing the extreme pressure and antiwear properties of the composition, without causing a corrosion effect which could be particularly detrimental to the functioning of the electric or hybrid vehicle.

A composition according to the invention therefore exhibits good extreme pressure and antiwear properties while at the same time being noncorrosive. It thus proves particularly advantageous for application, as contemplated by the invention, in a propulsion system of an electric or hybrid vehicle, where it is crucial to prevent the risks of corrosion while possessing good dielectric properties.

A composition according to the invention also has the advantage of being easy to formulate. It is possible more particularly, by using one or more noncorrosive phosphorus compounds according to the invention as an extreme pressure and antiwear additive, to remove the need to use additional “anticorrosion” additives in these lubricants, such additives being intended to inhibit the effects of corrosion that are brought about in particular by the use of corrosive additives.

The present invention also provides a method for lubricating a propulsion system of an electric or hybrid vehicle, comprising at least one step of contacting at least one mechanical component of said system with a lubricating composition comprising at least one phosphorus compound free from sulfur and from amine function as extreme pressure and antiwear additive.

A lubricating composition according to the invention is advantageously used to lubricate the electric motor itself, more particularly the rolling bearings situated between the rotor and the stator of an electric motor, and/or the transmission, more particularly the reduction gear, in an electric or hybrid vehicle.

Other features, variants and advantages of the use of a phosphorus compound free from sulfur and from amine function according to the invention will emerge more clearly from a reading of the description and the examples which follow, which are provided for the purpose of illustration and not to limit the invention.

In the text below, the expressions “of between . . . and . . . ”, “ranging from . . . to . . . ” and “varying from . . . to . . . ”, are equivalent and are intended to signify that the end points are included, unless otherwise stated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents schematically an electric or hybrid vehicle propulsion system.

DETAILED DESCRIPTION

Phosphorus Extreme Pressure and Antiwear Additives According to the Invention

As specified earlier on, the invention resides in the use, in a lubricant for the drive system of an electric or hybrid vehicle, as extreme pressure and antiwear additive, of one or more phosphorus compounds which are free from sulfur and from amine function.

In the text below, and unless indicated otherwise, the term “phosphorus additive (or compound) according to the invention” will be used to denote said phosphorus compound or compounds free from sulfur and from amine function, that are used according to the invention as an extreme pressure and antiwear additive.

“Free from sulfur” in the sense of the present invention is intended to characterize the fact that the extreme pressure and antiwear additive contemplated according to the invention does not comprise a sulfur atom.

“Free from amine function” in the sense of the invention is intended to characterize the fact that the extreme pressure and antiwear additive contemplated according to the invention does not comprise an amine function—that is, does not comprise any primary, secondary, tertiary or quaternary amine group.

The extreme pressure and antiwear additive contemplated according to the invention preferably does not comprise a nitrogen atom.

The phosphorus compounds according to the invention which are free from sulfur and from amine function endow the composition with extreme pressure and antiwear properties.

The phosphorus extreme pressure and antiwear additives according to the invention advantageously are not corrosive, meaning that they do not give rise to a corrosion effect when in contact with metallic surfaces, more particularly those of the components of a propulsion system in an electric or hybrid vehicle.

The phosphorus extreme pressure and antiwear additives used according to the invention may more particularly be selected from phosphoric acid derivatives and more particularly from phosphate esters, phosphite esters, phosphonate esters, phosphinate esters and phosphine oxides.

More particularly, the phosphorus extreme pressure and antiwear additives according to the invention may be of formula (I) below:

in which s is 0 or 1; and the radicals X represent, independently of one another, groups —OR′ or R′, where R′ represent hydrocarbon groups having preferably from 1 to 24 carbon atoms, with the proviso that, when s is 0, the three radicals X represent groups —OR′ and, when s is 1, at least two of the three radicals X represent groups —OR′.

According to one particular embodiment, the phosphorus extreme pressure and antiwear additive according to the invention is selected from phosphite esters, and conforms more particularly to the formula (I) above in which s is 0.

According to another particular embodiment, the phosphorus extreme pressure and antiwear additive according to the invention is selected from phosphonate esters, and conforms more particularly to the formula (I) above in which s is 1 and two of the three radicals X represent groups —OR′.

According to another particular embodiment, the phosphorus extreme pressure and antiwear additive according to the invention is selected from phosphate esters, and conforms more particularly to the formula (I) above in which s is 1 and the three radicals X represent groups —OR′.

The hydrocarbon groups R′ in the formula (I) above are preferably selected, independently of one another, from:

-   -   preferably C₁ to C₂₄ linear or branched alkyl groups;     -   preferably C₂ to C₁₈ linear or branched alkenyl groups;     -   preferably C₁ to C₂₄ alkoxyalkyl groups;     -   preferably C₃ to C₈ cycloalkyl groups;     -   preferably C₆ to C₁₀ aryl groups;         where said groups may themselves optionally be substituted by         one or more hydrocarbon groups, more particularly by one or more         alkyl, alkenyl, alkoxyalkyl, cycloalkyl and/or aryl groups.

In the context of the invention:

-   -   “alkyl” means a linear or branched saturated aliphatic group;         for example, a C_(x) to C_(z) alkyl represents a saturated         carbon chain of x to z carbon atoms which is linear or branched;     -   “alkenyl” means a linear or branched unsaturated aliphatic         group; for example, a C_(x) to C_(z) alkenyl group represents an         unsaturated carbon chain of x to z carbon atoms which is linear         or branched;     -   “alkoxyalkyl” means an alkyl group bearing at least one alkoxy         group. An alkoxy group is a group —OR in which R represents an         alkyl group;     -   “cycloalkyl” means a cyclic alkyl group; for example, a C_(x) to         C_(z) cycloalkyl represents a cyclic carbon group of x to z         carbon atoms, for example a cyclopropyl, cyclobutyl,         cyclopentyl, cyclohexyl or cycloheptyl;     -   “aryl” means a mono- or polycyclic aromatic group, more         particularly comprising between 6 and 10 carbon atoms. Examples         of aryl groups include the phenyl and naphthyl groups.

According to one preferred embodiment, the phosphorus extreme pressure and antiwear additives according to the invention are selected from phosphate esters of formula (I′) below:

in which R₁, R₂ and R₃ represent, independently of one another, hydrocarbon groups having preferably from 1 to 24 carbon atoms, more particularly as defined above.

Preferably R₁, R₂ and R₃ are selected, independently of one another, from preferably C₂ to C₁₈ linear or branched alkyl groups; preferably C₃ to C₈ cycloalkyl groups; and preferably C₆ to C₁₀ aryl groups; said cycloalkyl and aryl groups may optionally be substituted by one or more linear or branched alkyl groups.

According to one particular embodiment, a phosphorus extreme pressure and antiwear additive according to the invention is of formula (I′) above in which R₁, R₂ and R₃ are identical, preferably as defined above.

According to this embodiment, the phosphorus extreme pressure and antiwear additives according to the invention may advantageously be selected from triaryl phosphate esters, and especially tri(alkyl-aryl) phosphate esters, preferably from triphenyl phosphate esters. A phosphorus extreme pressure and antiwear additive according to the invention is preferably of formula (II) below:

in which the groups R represent, independently of one another, C₁ to C₁₀, more particularly C₃ to C₈, linear or branched alkyl groups and n, independently at each occurrence, represents 0, 1 or 2.

Preferably n=1 and R represents groups in para position, preferably C₃ to C₆, preferably branched, alkyl groups, such as an isopropyl group.

A phosphorus antiwear additive according to the invention is preferably of formula (II) in which the groups —(R)_(n) are identical.

According to another preferred embodiment, the phosphorus extreme pressure and antiwear additives according to the invention are selected from phosphite esters of formula (I″) below:

in which R₄, R₅ and R₆ represent, independently of one another, hydrocarbon groups, having preferably from 1 to 24 carbon atoms, more particularly as defined above.

Preferably R₄, R₅ and R₆ are selected, independently of one another, from preferably C₂ to C₁₈ linear or branched alkyl groups; preferably C₃ to C₈ cycloalkyl groups; and preferably C₆ to C₁₀ aryl groups; said cycloalkyl and aryl groups optionally being able to be substituted by one or more linear or branched alkyl groups.

According to one particular embodiment, a phosphorus extreme pressure and antiwear additive according to the invention is of formula (I′) above in which R₄, R₅ and R₆ are identical, preferably as defined above.

According to this embodiment, the phosphorus extreme pressure and antiwear additives according to the invention may advantageously be selected from triaryl phosphite esters, and especially tri(alkyl-aryl) phosphite esters, preferably from triphenyl phosphite esters.

A phosphorus extreme pressure and antiwear additive according to the invention is preferably of formula (II′) below:

in which the groups R represent, independently of one another, C₁ to C₁₀, more particularly C₃ to C₈, linear or branched alkyl groups and n, independently at each occurrence, represents 0, 1 or 2.

Preferably, n=1 and R represents groups in para position, preferably C₃ to C₆, preferably branched, alkyl groups, such as an isopropyl group.

A phosphorus antiwear additive according to the invention is preferably of formula (II′) in which the groups —(R)_(n) are identical.

The phosphorus antiwear additive according to the invention is advantageously selected from tri(isopropylphenyl) phosphate (CAS 68937-41-7) and tris(2,4-di-tert-butylphenyl) phosphite (CAS 31570-04-4).

It is understood, in the context of the present invention, that the phosphorus extreme pressure and antiwear additive contemplated according to the invention may take the form of a mixture of at least two phosphorus compounds, more particularly as defined above. Phosphorus compounds used according to the invention may be commercially available, or else prepared by synthesis techniques that are known to those skilled in the art.

The phosphorus extreme pressure and antiwear additive or additives contemplated according to the invention, more particularly as defined above, may be used in a lubricating composition for a propulsion system of an electric or hybrid vehicle at a rate of 0.01% and 10% by mass, preferably between 0.1% and 5% by mass, more preferably between 0.5% and 3% by mass, relative to the total mass of the lubricating composition.

According to one particularly preferred embodiment, the phosphorus extreme pressure and antiwear additive or additives used according to the invention are triaryl phosphate esters, more particularly of the formula (11) as defined above, and are preferably used at a rate of 0.01% and 10% by mass, preferably between 0.1% and 5% by mass, more preferably between 0/5% and 3% by mass, relative to the total mass of the lubricating composition.

According to another particularly preferred embodiment, the phosphorus extreme pressure and antiwear additive or additives used according to the invention are triaryl phosphite esters, more particularly of formula (I′) as defined above, and are preferably used at a rate of 0.01/% and 10% by mass, preferably between 0.1% and 5% by mass, more preferably between 0.5% and 3% by mass, relative to the total mass of the lubricating composition.

A lubricating composition contemplated according to the invention preferably comprises less than 10% by mass, more particularly less than 5% by mass, or is even free from, amine and/or sulfur antiwear additive(s), more particularly amine and/or sulfur additive(s) containing phosphorus.

A lubricating composition contemplated according to the invention advantageously comprises less than 7.5% by mass, more particularly less than 3% by mass, or is even free from, antiwear additive(s) different from the phosphorus additives free from sulfur and from amine function that are contemplated according to the invention.

Lubricating Composition

A composition used according to the invention may comprise, further to one or more phosphorus extreme pressure and antiwear additives according to the invention, more particularly as defined above, one or more base oils, and also other additives, which are conventionally contemplated in lubricating compositions.

Base Oil

A lubricating composition suitable for the invention may therefore comprise one or more base oils.

These base oils may be selected from base oils which are conventionally used in the field of lubricating oils, such as mineral, synthetic or natural, animal or plant oils or mixtures thereof.

The base oil may comprise a mixture of two or more oils—for example, a mixture of two, three or four base oils.

The base oils in the lubricating compositions contemplated according to the invention may more particularly be oils of mineral or synthetic origin that belong to groups I to V according to the classes defined in the API classification (or equivalents thereof according to the ATIEL classification) and presented in table 1 below, or mixtures thereof.

TABLE 1 Content of Sulfur Viscosity saturates content index (VI) Group I  <90%  >0.03% 80 ≤ VI < 120 Mineral oils Group II ≥90% ≤0.03% 80 ≤ VI < 120 Hydrocracked oils Group III ≥90% ≤0.03% ≥120 Hydrocracked or hydroisomerized oils Group IV Polyalphaolefins (PAO) Group V Esters and other bases not included in groups I to IV

The mineral base oils include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, deasphalting, solvent deparaffining, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.

Mixtures of synthetic and mineral oils, which may be biobased, may also be used.

There is generally no limitation as regards the use of different base oils for producing the compositions used according to the invention, apart from the fact that they must have properties—especially in terms of viscosity, viscosity index or oxidation resistance—that are suitable for use for propulsion systems of an electric or hybrid vehicle.

The base oils in the compositions used according to the invention may also be selected from synthetic oils, such as certain esters of carboxylic acids and alcohols, polyalphaolefins (PAO), and polyalkylene glycols (PAG) obtained by polymerizing or copolymerizing alkylene oxides comprising from 2 to 8 carbon atoms, more particularly from 2 to 4 carbon atoms.

The PAOs used as base oils are obtained, for example, from monomers comprising from 4 to 32 carbon atoms, as for example from octene or decene. The weight-average molecular mass of the PAO may vary quite broadly. The weight-average molecular mass of the PAO is preferably less than 600 Da. The weight-average molecular mass of the PAO may also range from 100 to 600 Da, from 150 to 600 Da, or else from 200 to 600 Da.

The base oil or oils in the composition used according to the invention is or are advantageously selected from polyalphaolefins (PAO), polyalkylene glycols (PAG), esters of carboxylic acids and alcohols, and mixtures thereof.

The base oil or oils in the composition used according to the invention is or are preferably selected from group III, IV or V oils and mixtures thereof, with preference being given to a group III base oil.

According to one alternative embodiment, the base oil or oils in the composition used according to the invention may be selected from group 11 base oils.

It is for those skilled in the art to adjust the amount of base oil to be used in a composition suitable for the invention.

A lubricating composition contemplated according to the invention may comprise at least 50% by mass of base oil(s), relative to its total mass, more particularly from 60 to 99% by mass of base oil(s), and very particularly between 70 and 98% by mass, preferably between 80 and 97% by mass.

Additional Additives

A lubricating composition suitable for the invention may further comprise any types of additives, other than the phosphorus extreme pressure and antiwear additives contemplated according to the invention, that are suitable for use in a lubricant for a propulsion system of an electric or hybrid vehicle.

It will be appreciated that the nature and the amount of additives used are selected so as not to adversely affect the properties of the lubricating composition, more particularly the properties imparted by the phosphorus extreme pressure and antiwear additive or additives according to the invention.

Such additives, which are known to those skilled in the art of the lubrication and/or cooling of propulsion systems of electric or hybrid vehicles, may be selected from friction modifiers, viscosity index modifiers, extreme pressure additives other than the phosphorus extreme pressure antiwear additives according to the invention, detergents, dispersants, antioxidants, pourpoint depressants, antifoams and mixtures thereof.

A composition suitable for the invention advantageously comprises at least one additional additive selected from antioxidants, detergents, dispersants, pourpoint depressants, antifoams, and mixtures thereof.

These additives may be introduced in isolation and/or in the form of a mixture of the kind already available for sale for commercial lubricant formulations for vehicle motors, with a level of performance as defined by the ACEA (Association des Constructeurs Européens d'Automobiles) and/or the API (American Petroleum Institute), which are well known to those skilled in the art.

A lubricating composition suitable for the invention may comprise at least one friction modifier additive. The friction modifier additive may be selected from a compound providing metallic elements and an ash-free compound. The compounds providing metallic elements include the complexes of transition metals such as Mo, Sb, Sn, Fe, Cu and Zn in which the ligands may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or phosphorus atoms. The ash-free friction modifier additives are generally organic in origin and may be selected from monoesters of fatty acids and polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, fatty epoxide borates; fatty amines or glycerol esters of fatty acid. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms.

A lubricating composition suitable for the invention may comprise from 0.01 to 2% by weight or from 0.01 to 5% by weight, preferably from 0.1 to 1.5% by weight or from 0.1 to 2% by weight of friction modifier additive, relative to the total weight of the composition.

A lubricating composition used according to the invention may comprise at least one antioxidant additive.

The antioxidant additive makes it possible generally to retard the degradation of the composition in service. This degradation may be manifested, in particular, in the formation of deposits, in the presence of sludges or in an increase in the viscosity of the composition. The antioxidant additives act in particular as radical inhibitors or hydroperoxide destroyers. The antioxidant additives commonly employed include phenolic antioxidant additives, amine-type antioxidant additives and phospho-sulfur antioxidant additives. Some of these antioxidant additives, such as the phospho-sulfur antioxidant additives, for example, may be ash generators. The phenolic antioxidant additives may be free from ash or else may be in the form of neutral or basic metal salts. The antioxidant additives may in particular be selected from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylammnes substituted by at least one C1-C12 alkyl group, N,N′-dialkyl-aryl-diamines, and mixtures thereof.

According to the invention, preferably, the sterically hindered phenols are selected from compounds comprising a phenol group in which at least one carbon vicinal to the carbon bearing the alcohol function is substituted by at least one C₁-C₁₀ alkyl group, preferably a C₁-C₆ alkyl group, preferably a C₄ alkyl group, preferably by the tert-butyl group.

The amine compounds are another class of antioxidant additives which can be used, optionally in combination with the phenolic antioxidant additives. Examples of amine compounds are aromatic amines, as for example the aromatic amines of formula NR⁴R⁵R⁶ in which R⁴ represents an aliphatic group or an aromatic group which is optionally substituted, R⁵ represents an aromatic group which is optionally substituted, and R⁶ represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R⁷S(O)_(z)R⁸ in which R⁷ represents an alkylene group or an alkenylene group, R⁸ represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.

Sulfurized alkyl phenols or their alkali metal and alkaline earth metal salts may also be used as antioxidant additives.

Another class of antioxidant additives is that of copper compounds, for example copper thio- or dithiophosphates, copper salts of carboxylic acids, and copper dithiocarbamates, sulfonates, phenates and acetylacetonates. Copper I and II salts and succinic acid or anhydride salts may also be used.

A lubricating composition used according to the invention may contain any types of antioxidant additives known to those skilled in the art.

A lubricating composition used according to the invention advantageously comprises at least one ash-free antioxidant additive.

A lubricating composition used according to the invention may comprise from 0.5 to 2% by weight of at least one antioxidant additive, relative to the total weight of the composition.

A lubricating composition suitable for the invention may also comprise at least one detergent additive.

The detergent additives generally make it possible to reduce the formation of deposits on the surface of metallic components by dissolving oxidation and combustion byproducts.

The detergent additives which can be used in a lubricating composition used according to the invention are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head.

The associated cation may be a metal cation of an alkali metal or alkaline earth metal.

The detergent additives are preferably selected from alkali metal or alkaline earth metal salts of carboxylic acids, sulfonates, salicylates, naphthenates, and phenate salts. The alkali metals and alkaline earth metals are preferably calcium, magnesium, sodium or barium.

These metal salts generally comprise the metal in a stoichiometric amount or else in excess, thus in an amount greater than the stoichiometric amount. They are then overbased detergent additives; the excess metal gives the detergent additive its overbased character and is then generally in the form of a metal salt which is insoluble in the oil, as for example a carbonate, a hydroxide, an oxalate, an acetate or a glutamate, preferably a carbonate.

A lubricating composition suitable for the invention may comprise, for example, from 2 to 4% by weight of detergent additive, relative to the total weight of the composition.

A lubricating composition used according to the invention may likewise comprise at least one dispersant.

The dispersant may be selected from Mannich bases, succinimides and derivatives thereof.

A lubricating composition used according to the invention may comprise, for example, from 0.2 to 10% by weight of dispersant, relative to the total weight of the composition.

A lubricating composition suitable for the invention may further comprise at least one antifoam.

The antifoam may be selected from silicones.

A lubricating composition suitable for the invention may comprise from 0.01 to 5% by mass, preferably from 0.1 to 2% by mass, of antifoam, relative to the total weight of the composition.

A lubricant composition suitable for the invention may also comprise at least one pourpoint depressant (PPD).

By slowing down the formation of paraffin crystals, the pourpoint depressants generally enhance the low-temperature behavior of the composition. Examples of pourpoint depressants include polyalkyl methacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and alkylated polystyrenes.

As regards formulation of a lubricating composition of this kind, said phosphorus antiwear additive or additives according to the invention may be added to a base oil or mixture of base oils, after which the other, complementary additives are added.

Said phosphorus extreme pressure and antiwear additive or additives according to the invention may alternatively be added to a conventional, pre-existing lubricating formulation, comprising in particular one or more base oils and optionally additional additives.

Said phosphorus extreme pressure and antiwear additive or additives according to the invention may alternatively be combined with one or more additional additives, and the additive “package” thus formed may be added to a base oil or mixture of base oils.

A lubricating composition used according to the invention advantageously has a kinematic viscosity, measured at 100° C. according to standard ASTM D445, ranging from 1 to 15 mm²/s, more particularly ranging from 3 to 10 mm²/s.

A lubricating composition used according to the invention advantageously has a kinematic viscosity, measured at 40° C. according to standard ASTM D445, ranging from 3 to 80 mm²/s, more particularly ranging from 15 to 70 mm²/s.

A lubricating composition used according to the invention may advantageously have a grade according to the SAEJ300 classification that is defined by the formula (X)W(Y), in which X represents 0 or 5; and Y represents an integer ranging from 4 to 20, more particularly ranging from 4 to 16 or from 4 to 12.

A lubricating composition used according to the invention advantageously has an electrical resistivity measured at 90° C. of between 5 and 10 000 Mohm·m, more preferably between 6 and 5000 Mohm·m.

Moreover, a lubricating composition used according to the invention advantageously exhibits a dielectric loss measured at 90° C. of between 0.01 and 30, more preferably between 0.02 and 25, very preferably between 0.02 and 10.

According to one preferred embodiment, a lubricating composition formulated according to the invention comprises or even consists of:

-   -   a base oil, or mixture of base oils, preferably selected from         group III base oils and group IV or V base oils;     -   one or more phosphorus compounds free from sulfur and from amine         function, more particularly as defined above, preferably of         triaryl phosphate ester type, more particularly conforming to         the formula (II) as defined above;     -   optionally one or more additional additives, selected from         antioxidants, detergents, dispersants, pourpoint depressants,         antifoams, and mixtures thereof.

A lubricating composition formulated according to the invention preferably comprises or even consists of:

-   -   from 0.1% to 5% by mass, more particularly from 0.5 to 3% by         mass, of one or more phosphorus compounds free from sulfur and         from amine function, preferably selected from triaryl phosphate         esters, more particularly conforming to the formula (II) as         defined above, and triaryl phosphite esters, more particularly         conforming to the formula (II′) as defined above, more         preferably selected from tri(isopropylphenyl) phosphate and         tris(2,4-di-tert-butylphenyl) phosphite;     -   from 50% to 99.5% by mass, more particularly from 60 to 99% by         mass, of one or more base oils, preferably selected from group         III base oils, group IV or V base oils, and mixtures thereof;         and     -   optionally from 0.1 to 5% by mass of one or more additives         selected from antioxidants, detergents, dispersants, pourpoint         depressants, antifoams, and mixtures thereof; where the amounts         are expressed relative to the total mass of said lubricating         composition.

Application

As indicated previously, a composition formulated according to the invention, as described above, is used as a lubricant for a propulsion system of an electric or hybrid vehicle, and more particularly for the motor and the power electrics in an electric or hybrid vehicle.

The present invention therefore concerns the use of a composition as defined above, employing as extreme pressure and antiwear additive, preferably as sole extreme pressure and antiwear additive, one or more phosphorus compounds free from sulfur and from amine function, more particularly as defined above, preferably of triaryl phosphate ester type, more particularly conforming to the formula (II) as defined above, for lubricating a propulsion system of an electric or hybrid vehicle, more particularly for lubricating the electric motor and the power electrics of an electric or hybrid vehicle.

The present invention thus concerns the use, as additive in a lubricating composition, of one or more phosphorus compounds free from sulfur and from amine function, more particularly as defined above, for simultaneously reducing the wear and causing no corrosion of the components of a propulsion system of an electric or hybrid vehicle, more particularly of the winding of the stator and rotor, of the sensors in the propulsion system or of the solenoid valves in the hydraulic system, but also of the rolling bearings situated between the rotor and the stator of an electric motor and/or of the transmission, more particularly the reduction gear, in an electric or hybrid vehicle.

As represented schematically in FIG. 1 , the propulsion system of an electric or hybrid vehicle comprises, in particular, the electric motor part (1), an electric battery (2) and a transmission, more particularly a speed reduction gear (3).

The electric motor typically comprises power electronics (11) connected to a stator (13) and a rotor (14). The stator comprises coils, more particularly copper coils, which are supplied with an alternating electric current. This enables the generation of a rotating magnetic field.

The rotor in turn comprises coils, permanent magnets or other magnetic materials, and is made to rotate by the rotating magnetic field.

A rolling bearing (12) is generally incorporated between the stator (13) and the rotor (14). A transmission, and more particularly a speed reduction gear (3), allows the speed of rotation at the outlet of the electric motor to be reduced and the speed transmitted to the wheels to be adapted, so making it possible at the same time to control the speed of the vehicle.

The rolling bearing (12) is subject in particular to high mechanical stresses and gives rise to problems of wear by fatigue. It is therefore necessary for the rolling bearing to be lubricated in order to increase its working life. The reduction gear as well is subject to high frictional stresses and therefore requires appropriate lubrication so that it is not damaged too rapidly.

Accordingly, the invention relates more particularly to the use of a composition as described above for lubricating an electric motor of an electric or hybrid vehicle, more particularly for lubricating the rolling bearings situated between the rotor and the stator of an electric motor. It also relates to the use of a composition as described above for lubricating the transmission, more particularly the reduction gear, in an electric or hybrid vehicle.

Advantageously, a composition according to the invention may therefore be used for lubricating the various components of a propulsion system of an electric or hybrid vehicle, more particularly the rolling bearings situated between the rotor and the stator of an electric motor and/or the transmission, more particularly the reduction gear, in an electric or hybrid vehicle.

Advantageously, as set out above, a lubricating composition according to the invention exhibits excellent extreme pressure and antiwear performance while being noncorrosive. According to another of its aspects, the invention also relates to a method for lubricating at least one component of a propulsion system of an electric or hybrid vehicle, more particularly the rolling bearings situated between the rotor and the stator of an electric motor; and/or the transmission, more particularly the reduction gear, comprising at least one step of contacting said at least one component with a composition as described above.

The present invention thus proposes a method for simultaneously reducing the wear and not causing corrosion of the at least one component of a propulsion system of an electric or hybrid vehicle, more particularly the rolling bearings situated between the rotor and the stator of an electric motor; and/or the transmission, more particularly the reduction gear, said method comprising at least one step of contacting said at least one component with a composition as described above.

The entirety of the features and preferences described for the composition used according to the invention and also for the uses thereof are also applicable to this method.

It may also prove advantageous to provide the various components of the propulsion system with electrical insulation.

Therefore, according to one particular embodiment, a composition according to the invention may exhibit good electrical insulation properties as well as lubrication properties.

According to this embodiment, a composition according to the invention may simultaneously be used for lubricating one or more components of a propulsion system of an electric or hybrid vehicle, more particularly for lubricating the sensors and solenoid valves of the motor, the rolling bearings, but also the winding situated at the rotor and the stator of an electric motor, or else the lubrication of the transmission, more particularly of the gears, sensors, solenoid valves, or else the reduction gear that is found in an electric or hybrid vehicle, and for providing at least one component of said propulsion system with electrical insulation, especially the battery, the motor or else the power electronics.

In the context of a variant implementation of this kind, a lubricating composition contemplated according to the invention advantageously has a kinematic viscosity, measured at 100° C. according to standard ASTM D445, of between 2 and 8 mm²/s, preferably between 3 and 7 mm²/s.

It will be appreciated that the uses described above may be combined: a composition as described above may be used as a lubricant, as an electrical insulant and also as a cooling fluid for the motor, the battery and the transmission of an electric or hybrid vehicle.

According to the invention, the particular, advantageous or preferred characteristics of the composition according to the invention permit the definition of uses according to the invention which are likewise particular, advantageous or preferred.

The invention will now be described by means of the following examples, which are of course given for the purpose of illustration and not to limit the invention.

Example

Various compositions were evaluated:

-   -   a composition C1 comprising a phosphorus compound A compliant         with the invention: tri(isopropylphenyl) phosphate;     -   a composition C2 comprising a phosphorus compound B compliant         with the invention tris(2,4-di-tert-butylphenyl) phosphite;     -   a composition C3 comprising a known phospho-sulfur compound C as         extreme pressure and antiwear compound, not compliant with the         invention: triphenyl phosphorothionate; and     -   a composition C4 comprising a mixture of known amine and         phosphate compounds D as antiwear compounds, not compliant with         the invention, sold under the name Irgalube 349;     -   a composition C5 comprising a mixture of known         dimercaptothiadiazole compounds E as antiwear compounds, not         compliant with the invention;     -   a composition C6 comprising a mixture of known zinc         dialkyldithiophosphate compounds F as antiwear compounds, not         compliant with the invention.

As well as each of the aforesaid compounds, compositions C1 to C6 comprise a group III base oil.

The compositions and the amounts (expressed as percentages by mass) are indicated in table 2 below.

TABLE 2 Composition C1 C2 C3 C4 C5 C6 Base oil 98% 98% 98% 98% 98% 98% Phosphorus compound A  2% — — — — — Phosphorus compound B —  2% — — — — Phospho-sulfur compound C — —  2% — — — Mixture of amine phosphates D — — —  2% — — Mixture of dimercaptothiadiazoles E — — — —  2% — Mixture of zinc dialkyldithiophosphates F — — — — —  2%

Evaluation of Corroding Power

Evaluation Method

The corrosive (or corroding) power of a composition may be evaluated by a test which entails studying the change in the electrical resistance value of a copper wire having a predetermined diameter as a function of the time of immersion of this wire within the composition. The change in the value of this electrical resistance is correlated directly with the variation in the diameter of the test wire. In the context of the present invention, the diameter of the wire selected is 70 μm.

In the present case, a copper wire is immersed in a test tube containing a volume of 20 mL of a test composition (where compositions C1 and C2 are compositions according to the invention and compositions C3 to C6 are compositions employed for comparison).

The resistance of the wire is measured by means of an ohmmeter.

The measuring current is 1 mA.

The temperature of the test composition is brought to 150° C.

The resistance of the copper wire is calculated by this equation (1):

$\begin{matrix} {R = {\rho \times \frac{L}{S}}} & \left\lbrack {{Math}.1} \right\rbrack \end{matrix}$

where R is the resistance, ρ is the resistivity of copper, L is the length of the wire, and S is the cross-sectional surface area.

In this equation (1), ρ and L are constants. The resistance R is therefore inversely proportional to the cross-sectional surface area of the immersed wire.

The diameter of the wire is calculated from the cross-sectional surface area (2):

$\begin{matrix} {S = {\frac{\pi}{4} \times D^{2}}} & \left\lbrack {{Math}.2} \right\rbrack \end{matrix}$

where D is the diameter of the wire.

Equation (2) is inserted into (1) in order to give the relation between the resistance and the diameter (3):

$\begin{matrix} {R = {\rho \times \frac{L}{\frac{\pi}{4} \times D^{2}}}} & \left\lbrack {{Math}.3} \right\rbrack \end{matrix}$

Accordingly, when the wire is corroded by the test compositions, the diameter of the wire falls, thereby causing an increase in the resistance value.

By monitoring the resistance, the change in diameter of the wire is monitored, which is a snapshot of the corrosion undergone by the immersed wire.

The loss of diameter of the wire is therefore calculated directly from the measured resistance.

When the measured resistance is infinite, an open circuit is present. This therefore means that the wire has broken, defining very severe corrosion.

Results

The results are summarized in table 3 below, and are expressed in μm (loss of diameter).

The lower the value obtained, the better the anticorrosion properties of the composition evaluated.

A composition is considered to be “noncorrosive” when the loss of diameter of the copper wire studied is less than or equal to 0.5 μm after immersion for 80 hours, more particularly less than or equal to 0.1 μm after immersion for 20 hours, in the composition.

TABLE 3 Composition C1 C2 C3 C4 C5 C6 Loss of 0 0.14 0.75 0.23 0.29 wire diameter (in broken μm) at 20 hours Loss of 0.10 0.21 1.80 0.58 wire wire diameter (in broken broken μm) at 40 hours Loss of 0.23 0.26 2.00 0.99 wire wire diameter (in broken broken μm) at 60 hours Loss of 0.31 0.48 2.18 1.51 wire wire diameter (μm) broken broken at 80 hours

It is apparent from these results that the addition of a phosphorus additive free from sulfur and from amine function according to the invention is not accompanied by a corrosive effect, in contrast to sulfur-containing or amine-containing phosphorus antiwear additives. 

1-10. (canceled)
 11. A method of improving the anti-wear properties of a lubricant composition for a propulsion system of an electric or hybrid vehicle, comprising: adding at least one phosphorus compound to a lubricant composition for lubricating the propulsion system, wherein the at least one phosphorous compound is free of sulfur and amine functional groups.
 12. The method of claim 11, wherein the at least one phosphorus compound is selected from phosphate esters, phosphonate esters, phosphinate esters, phosphite esters, phosphine oxides, or a combination thereof.
 13. The method of claim 11, wherein the at least one phosphorus compound is selected from compounds of formula (I) below:

wherein: s is 0 or 1; and each X group is independently selected from —OR′ or R′ groups, wherein R′ represents a hydrocarbon group having from 1 to 24 carbon atoms; when s is 0, each X group is an —OR′ group; and when s is 1, at least two of the X groups are —OR′ groups.
 14. The method of claim 11, wherein the at least one phosphorus compound is selected from phosphate esters of formula (II) below:

wherein: each R group is independently selected from linear or branched, C₁ to C₁₀ alkyl groups; and each n is independently selected from 0, 1 or
 2. 15. The method of claim 14, wherein: each n is 1; and each R group is a branched C₃ to C₆ alkyl group in a para position.
 16. The method of claim 11, wherein the at least one phosphorus compound is tri(isopropylphenyl) phosphate.
 17. The method of claim 11, wherein the at least one phosphorus compound is selected from phosphite esters of formula (II′) below:

wherein: each R group is independently selected from linear or branched, C₁ to C₁₀ alkyl groups; and each n is independently selected from 0, 1 or
 2. 18. The method of claim 17, wherein: each n is 1; and each R group is a branched C₃ to C₆ alkyl group in a para position.
 19. The method of claim 11, wherein the at least one phosphorus compound is tris(2,4-di-tert-butylphenyl) phosphite.
 20. The method of claim 11, wherein the lubricant composition comprises from 0.01% and 10% by mass of the at least one phosphorus compound, relative to the total mass of the lubricant composition.
 21. The method of claim 11, wherein the lubricant composition comprises from 0.5% and 3% by mass of the at least one phosphorus compound, relative to the total mass of the lubricant composition.
 22. The method of claim 11, wherein the lubricating composition comprises at least one base oil selected from polyalkylene glycols, polyalphaolefins, esters of carboxylic acids, alcohols, or a combination thereof.
 23. A method of reducing wear in in a propulsion system of an electric or hybrid vehicle, the method comprising lubricating and/or cooling an electric motor and/or power electronics of the electric or hybrid vehicle with a lubricant composition comprising at least one phosphorus compound that is free from sulfur and amine functional groups.
 24. The method of claim 23, wherein the at least one phosphorus compound comprises tri(isopropylphenyl) phosphate, tris(2,4-di-tert-butylphenyl) phosphite, or a combination thereof.
 25. The method of claim 23, further comprising lubricating rolling bearings located between a rotor and a stator of the electric motor with the lubricant composition.
 26. The method of claim 23, further comprising lubricating a reduction gear of a transmission of the electric or hybrid vehicle with the lubricant composition.
 27. The method of claim 23, wherein the lubricating composition comprises, relative to the total mass of the lubricating composition: from 0.1% to 5% by mass of the at least one phosphorus compound; from 50% to 99.5% by mass of at least one base oil selected from group III base oils, group IV base oils, group V base oils, or a combination thereof; and optionally from 0.1 to 5% by mass of at least one additive selected from antioxidants, detergents, dispersants, pourpoint depressants, antifoam agents, or a combination thereof.
 28. The method of claim 27, wherein: the lubricating composition comprises from 0.5 to 3% by mass of the at least one phosphorus compound; the at least one phosphorus compound is selected from tri(isopropylphenyl) phosphate, tris(2,4-di-tert-butylphenyl) phosphite, or a combination thereof; and the lubricating composition comprises from 60 to 99% by mass of the at least one base oil. 